STOCK-BASED COMPENSATION PLANS - stock-based compensation expenses (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Total stock based compensation expense	$ 533	$ 730	$ 1,042	$ 1,806
Cost of revenue
Total stock based compensation expense	12	13	42	22
Sales and marketing expense
Total stock based compensation expense	48	13	78	45
General and administrative
Total stock based compensation expense	$ 473	$ 704	$ 922	$ 1,739